Fix failing repo test
Fix failing repo test

After docker was added as a content_format, the tests were not passing.
This patch updates the test so that it no longer expects a specific list
of possible values but only verifies that the error message has some
options.

pombredanne/product-definition-center,tzhaoredhat/automation,maxamillion/product-definition-center,maxamillion/product-definition-center,product-definition-center/product-definition-center,pombredanne/product-definition-center,lao605/product-definition-center,lao605/product-definition-center,tzhaoredhat/automation,puiterwijk/product-definition-center,release-engineering/product-definition-center,xychu/product-definition-center,tzhaoredhat/automation,xychu/product-definition-center,release-engineering/product-definition-center,maxamillion/product-definition-center,product-definition-center/product-definition-center,release-engineering/product-definition-center,product-definition-center/product-definition-center,xychu/product-definition-center,pombredanne/product-definition-center,xychu/product-definition-center,product-definition-center/product-definition-center,pombredanne/product-definition-center,lao605/product-definition-center,puiterwijk/product-definition-center,tzhaoredhat/automation,lao605/product-definition-center,puiterwijk/product-definition-center,release-engineering/product-definition-center